No, that would be stupid. Well scientists believe that you, and I, — even the scientists themselves — are all doing this.
I’m really not. Yes, you are. It’s in your poop.
Metals are used in practically every product we use. Even detergents and shampoos have traces of them. Nanoparticles are used to limit body odour in socks, for instance. A lot of this is absorbed by the body and discarded as waste, which enters the sewage system and treatment plants.
So I could have been a millionaire by now? Since the idea isn’t to sift through individual toilet refuse, no, you would still probably be where you are now. To actually mine the sewage, wastewater is treated through physical, biological and chemical processes, resulting in treated water and biosolids. The biosolids, says US researchers, may be as good as a gold mine.
As good as a mine? Even better actually, in two ways. One, an earlier study in the journal Environmental Science and Technology found the levels of precious metals in municipal sludges in the US were comparable with that found in commercial mines. This makes actual treatment of sewage to reuse mined metals a viable option. Two, industrial miners use powerful chemicals called leachates to pull metals out of the ground. This method has ecological consequences. The same leachates need to be used when mining sewage, but here it can be done in controlled settings in a treatment plant with its effect on nature being limited.
Is this being done already? No. In countries where sewage is treated thoroughly, most biosolids produced at the end of the process is used as fertiliser. The remaining is sent to a landfill or burnt. The recent scientific results are interesting because, generally, sewage has been screened for harmful heavy chemicals such as cadmium or arsenic. No one’s actually tested to see whether there was something in all that waste that could actually be re-used, until now.
How big is this discovery? The older study, the one published in the journal, tested samples from 94 wastewater treatment plants across the US. Results showed most samples were rich in silver, gold and platinum-group metals. The authors of the most recent study extrapolated the data from those 94 tests to estimate that annually, an American city with about a million residents would produce enough waste that contains $13 million worth of metals. To break it down further, the eight-year study found that 1kg of sludge contained about 0.4mg gold, 28mg of silver, 638mg copper and 49mg vanadium.
This is ingenious. Yes, but digging through waste to find wealth is not new.
Yes, reuse, recycle — I know the mantra. There’s a lot more happening out there. Sewage plants are already removing nitrogen and phosphorous, key plant fertilisers. A Tokyo plant has already started extracting gold from sludge and says the process beats mining hands down. In Sweden, a treatment plant is experimenting with making bioplastics. And Singapore, quite famously, has its toilet-to-tap concept for drinking water.
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